Disposable syringe equipment which has a given amount of medication contained in the barrel is used extensively not only for saving the time required to have the medication transferred from an ampule into the barrel before injection but also for eliminating the potential hazard of infection with pathogenic bacteria and viruses due to the repeated use of the equipment.
Syringe equipment of this kind has the following basic construction: a cap is fitted on the needle attaching portion at the foremost end of the barrel and a plunger is inserted into the barrel from the rear end in such a way that a closed space is formed in front of the plunger, with a given amount of medication being contained in that space. Since one only need remove the cap and attach the needle to perform injection, the equipment has the advantage of providing great ease in handling.
The equipment, however, has a problem that originates from its simple construction; it adopts no closing means other than the cap which is detachably fitted on the needle attaching portion, so even if a malicious person ejects a portion of the medication or mixes it with a foreign matter or even replaces it with another medication, there is no way to check these acts as long as the cap is refitted.
A second problem with the equipment comes from the fact that it cannot be sterilized or disinfected just prior to use, which is in sharp contrast with another conventional type of syringe equipment that uses medications in ampules. Under the circumstances, it is necessary that the equipment of interest be distributed and stored in a sterilized atmosphere throughout the period from the filling of the medication in a sterile condition up to the time of actual use; to meet this need, the equipment must be wrapped with airtight packages and handled under strict control, this requiring cumbersome procedures.
To solve the first mentioned problem, the assignee previously proposed that the foremost end portion of the barrel and the cap are covered with a tubular continuous sealing device that is made of a heat-shrinkable film and which shrinks under heat to come into intimate contact with the outer peripheral surfaces of the foremost end portion of the barrel and the base portion of the cap, as well as the shoulder portion of the same (see the official gazette of Unexamined Published Japanese Utility Model Application Hei 3-101960).
According to this proposal, the sealing device prevents unauthorized removal of the cap and the plunger cannot be withdrawn since the medication filled space is closed (in vacuum). This offers the advantage of assuring freedom from anxiety for the user since he can verify that the syringe equipment has been properly sealed until use.
On the other hand, both the interior of the barrel at the basal end and the plunger rod remain exposed and provide areas for deposition of bacteria, viruses, as well as dirt or dust particles. To deal with this problem, the whole part of the syringe equipment must be wrapped with airtight packaging means. Thus, means for solving the aforementioned second problem is yet to be developed.
The sealing device proposed in Unexamined Published Japanese Utility Model Application Hei 3-101960, supra has another problem in that the cap must be shrunk sufficiently to assure strong adhesion to the outer peripheral surface of the barrel so that nobody can perform a misconduct by pulling the sealing device away from the barrel together with the cap and by then refitting it over the barrel. To meet this need, one may apply heat either at high temperatures for a short period or at comparatively low temperatures for a long period but, then, the medication in the barrel can potentially receive adverse thermal effects or the thermal expansion mismatch between the barrel, the plunger and the cap will cause gaps to form between these parts, which can potentially provide leaks for the medication.
If the medication in the barrel is a liquid of high viscosity, there is the need to use a fairly thick needle so that the medication of interest can be injected smoothly. To meet this need, it is often practiced that an anesthetic is aspirated into the barrel through the needle and injected into the patient, thereby alleviating the pain the patient may suffer during subsequent injection of the medication at the site of target.
A need also exists in certain cases for adding other substances than the medication of interest, as illustrated by the addition of another medication in liquid form immediately before the contained medication which is liquid form is injected or by the addition of a solubilizer just before the injection of the contained medication which is a powder, thereby rendering it in liquid form.
In these cases where another medication or the like that are in liquid form is (which are hereunder collectively referred to as the "additional liquid") to be added to the preloaded drug, the plunger must be moved in the direction for pulling it out of the barrel. However, with syringe equipment of the type contemplated by the invention which is filled with a given amount of medication, the barrel does not have graduations for reading the volume of the medication because there is no need to provide such graduations. Instead, the amount by which the plunger is withdrawn is measured visually to estimate the amount by which the additional liquid has been aspirated.
Under the circumstances, even if the plunger is designed to be longer than the predicted distance over which it is to be moved for aspirating the additional liquid, the foremost end of the plunger which has been located in a predetermined position may sometimes be moved backward of the position in which it was located at the time of filling in the medication if it is moved by a more-than-necessary large amount.
Those areas of the inside of the barrel which contact the plunger and the medication can be kept sterile throughout the period from the stages of distribution and storage up to the start of use. The area of the inside of the barrel which is backward of the plunger can also be kept sterile at the stages of distribution and storage since it is packed sterile by the sealing device; however, if the seal is opened to use the syringe, pathogenic bacteria and viruses may find the chance to adhere to the inner surfaces of that area. If the plunger is withdrawn up to the point where its foremost end reaches the area contaminated by the deposits of pathogenic bacteria and viruses, the medication will contact them and the patient can potentially be infected by the injection of the contaminated medication.
Thus, the first problem to be solved by the present invention is that the conventional syringe equipment which has a cap fitted on the needle attaching portion at the foremost end of the barrel and which has a plunger fitted in the barrel from the rear end to a predetermined position, with a medication being contained in the barrel, has had no sealing means available that can be applied easily without involving the aforementioned disadvantages, thereby attaining both purposes of preventing the malicious unauthorized use of the syringe and keeping it sterile at all stages up to its use.
The second problem to be solved by the present invention is that with said conventional syringe equipment, even the use of a plunger of considerable length does not eliminate the potential risk that if a medication in liquid form other than the one that is preliminarily contained in the barrel is aspirated for injection, pathogenic bacteria or viruses may contaminate the medication which is eventually administered to the patient.
Therefore, the first object of the invention is to insure that medication filled syringe equipment can be kept sterile at all stages until use, is protected against malicious unauthorized use, can be packaged in a simpler way and can protect the medication to be in a stable form.
The second object of the invention is to insure that an additional liquid such as an anesthetic, another medication in liquid form or a solubilizer can be aspirated by medication filled syringe equipment in an aseptic appropriate manner before injection.